1. Field of the Invention
The present invention relates to a wiring board, a stacked battery device, and a vehicle having the stacked battery device. More particularly, the present invention relates to an integrally-formed wiring board, a stacked battery device with the wiring board mounted thereon, and a vehicle that incorporates the stacked battery device.
2. Description of the Related Art
In recent years, electric vehicles and hybrid powered automobiles have actively been developed in the automotive industry with an aim of protecting the environment.
Secondary batteries to be employed by automobiles are required to be capable of outputting a high power. Hence, stacked batteries each formed by stacking a plurality of secondary cells (hereinafter, each secondary cell is referred to as “unit cell”) connected in series are employed.
As unit cells in a stacked battery differ from one another in internal resistance and capacity, in a state of being connected in series, the unit cells take different voltage shares. When the voltage shares vary, an excessive load is applied on a unit cell that takes a large voltage share. In such a state, the larger the voltage share taken by a unit cell, the more quickly the unit cell is degraded, resulting in that the unit cell that takes a large voltage share limits a usable life of the stacked battery.
To solve such a problem, it is desirable to measure the voltage shares taken by the unit cells and control the voltage shares based on a result of measurement, thereby equalizing all the voltage shares taken by the unit cells.
An invention that allows detection of a voltage of each unit cell; i.e., a voltage share, from the outside of a battery is described in Japanese Patent Application Laid-open No. 2005-235428. The invention described in Japanese Patent Application Laid-open No. 2005-235428 is specifically described below. Tabs are connected to a collector foil of each unit cell such that positions of the tabs differ from one unit cell to another. The plurality of unit cells and a wiring plate that includes contacts at positions corresponding to the tabs are stacked. The tabs are brought into contact with the corresponding contacts to derive an output voltage of each unit cell to the outside of the battery via the wiring board.
However, the invention described in Japanese Patent Application Laid-open No. 2005-235428 is disadvantageous in that, a separator, which is a constituent element of the unit cell, can be deformed when the tab (specifically, a metal plate or a metal foil) is inserted between layers in the battery for connecting the tabs with the collector foil. As the tab is formed of a metal plate or a metal foil, stress can concentrate on a connecting portion between the tab and the collector or that between the tab and the wiring board formed with a flexible substrate, inducing metal fatigue of the tab which can be caused by vibrations.
The present invention has been achieved to solve the above problems and is to provide a wiring board for battery control that allows monitoring of individual output voltages of unit cells while attaining a high reliability, a stacked battery device, and a vehicle having the stacked battery device.